Method of brazing heating coils



March 25,1930.

A. T. LEWIS ET AL METHOD OF BRAZING HEATING COILS Filed March 1928 2 Sheets-Sheet l March 25, 1930. A. T. LEWIS ET AL METHOD OF BRAZING HEATING COILS Filed March 9, 1928 2 Sheets-Sheet 2 Patented Mar. 25, 1930 UNITED STATES PATENT OFFICE ALEXANDER THORNTON LEWIS AND DONALD E. FRENCH, OF MRIION, PENNSYIVANIA,

ASSIGNOBS TO YORK HEATING AND VENTILATING CORPORATION, OF PHILADEL- PHIA, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA METHOD OF BRAZING- HEATDNG GOILS Application filed March 9, 1928. Serial Nb. 260,458.

The present invention relates to heating apparatus and more particularly to a heatin coil of unitary construction and the metho of making the same.

Some of the objects of the resent.invention are to provide an improve heating coil; to rovide a heating coil consisting of tubes and headers having the ends of the tubes integrally' united thereto; to provide apipe coil heating unit so arranged and constructed that the stress and strains caused by expansion and contraction are automatically absorbed and have no efiect uponthe joint between the pipes or tubes and the headers; to

provide a method of successfully jointing at high temperature the ends of tubes to a header; to provide a method of jointing finned tubes and headers at a temperature higher than the annealing point of the tube or fin and higher than the fusing point of any material used for bonding the fins to the tubes; to provide a method of successfully uniting copper tubes or tubes of metal other than iron or steel to steel or iron headers at a temperature approximating the fusing point of copper or metal other than steel or iron;

to provide a finned tube construction wherein a'tube or tubes can be integrall attached to a steel header without the use 0 solder or tin- 0 ning; to provide a coil structure for indirect heating units wherein a maximum heating surface and a maximum passage for air are obtained; and to rovide other improvements as will hereina er appear.

In the accompanying drawings, Fi 1 represents a plan of a heating coil em odying one form of the present invention; F1 2 represents a side elevation of the same; 3 represents an end elevation of Flg. 1; Fig. 4 represents an enlarged detail showing the tube pitch of the unit when placed in a vertical position; and Fig. 5 represents a sectional detail of the tube construction after the uniting 0 eration.

Re err-ing to the drawings, one form of the present invention comprises a heating coil consisting enerally of an inlet header 10, an outlet hea er 11, and interconnecting heater tubes 12 through which the heating medium is circulated. In the. present instance, the

headers 10 and 11 are steel, while the tubes 12 are of copper, though it will be understood the invention is not specifically limited to these two metals but might be applied or embodied in other heating units having headers and tubes. It should also be noted that Fig. {5 illustrates the heating unit of the present invention in its vertical position, in which case one header is staggeredhorizon tally with.

respect to the other so that there is a free gravity flow of an liquid inzthe tubes 12'for return purposes, t oughsuch staggered relation of the headers is unnecessary where the unit is mounted in a horizontal position because the natural pitch of the tubes allows for the desired return;

The headers 10 and 11, respectiv ly, consist of header plates Band 14' provi ed with through holes15 and 16' (here shown as of the same size because the tubes are preferably ofthe same diameter) for the reception of the respective tubes 12, and casings 17 and 18 of tubular form which are respectively attached to the header plates 13 and 14 in a leak proof manner, such as by welding thereto, as shown at 19. The size of the casing 17 is such as to provide a chamber 20 which communicates with all of the inlet ends of the tubes 12, while the casing 18 is of such a size as to provide a chamber 21 communicating with all of the outlet ends of the tubes 12. At a convenient point, the casing 17 is provided with an inlet nipple 22, and similarly the casing 18 is provided with an outlet nipple 23, these two nipples 22 and'23 establishin circulating connections for the heating me ium. By reference to Fig. 2, it will be seen that each tube 12 leaves a common inlet header 10, extends outwardly therefrom, with a slight downward pitch for a predetermined distance, then makes a reverse bend or loop 2 1 and returns with substantially the same downward pitch to the outlet header 11. For maximum tube area with maximum air circulating space, one row of the tube inlets 15 is staggered with respect to the other row oi inlets 15, and one row of 'tube outlets 16 is staggered with respect to the other row of tube outlets, and in this instance the staggered distance in each case is substantially equal to the outside diameter of a tube. As a result, all of the tube returns or loops 24 at both ends are substantially in contact with each other at opposite sides while the body the arc of the loops 24, while the spaces 25 are variable in accordance with the distances between the holes in the header, but whatever the variation in dimensions there is always an unrestricted tortuous path between the pipe coils for the passage of air in contact with the fins 28 which are mounted upon the length of each tube between the loo ends. While this construction provides an e ective heat absorbing path for the air, it also furnishes an efiective, means for automatically compensating for expansion and contraction of the tubing due to changes of temperature. Thus because the two headers are located substantially adjacent one another and are interconnected by substantially U-shaped tubes, the joints between the tubes and headers are not subjected to expansion strains and stresses because the body of each of the tubes is free to move and automatically adjust itself to a change in temperature.

In order to form a leak proof joint between the tube ends and the headers and'to provide a joint which units the parts with an integral construction, each tube 12 has its ends insorted in the respective holes 15 and 16 of the header plates 13 and 14 with a clearance fit, while the annular marginal edges of the respective tubes preferably project slightly beyond the plane of the outer face of the header plates. Also it should be noted that the holes 13 and 14 are counter-bored on the outer face of each header to form annular grooves 29 for the reception of the bonding material. When the tubes have been as sembled in the header plates '13 and 14 with 'their ends protruding through the counterbore grooves 29, each is successively subjected to the action of a welding torch simultaneously with the application of a bonding material to the joint between the tubes and plates. This bonding material is preferably an alloy, such as bronze, though it may be any other suitable bonding material which has a fusing point approximating the fusing point of copper or other material of which the tube is made. The uniting action, therefore, takes place at a temperature substantially that of the fusing point of copper, and as a result each tube is joined to its plate by an annular ring 27 formed as an integral part of the plate by the simultaneous fusing of the bonding material and the material of the plate.

Since one of the main features of the present invention is the formation of a joint at a relatively high temperature, say for example a temperature not less than 1400 F., it "is evident that the desired uniting of the tube and header cannot ordinarily take place,

without damage either to the tube, or in case of finned tubes to the fins, and to the joint between the fins and the tubes. To the end, therefore, that this uniting operation can be successfully carried out without damage to the tubes, the fins or the bonding material between the tubes and fins, the present invention embodies as a new step in joint construction the use of a bonding material which has a fusing point as near as possible to the fusing point of the material of the tubes. This fusing point of this bonding material should not only be well above the annealing point of the tube'material but also well above the annealing point of the material of the fins of a tube in case a finned type of tube is to be united to a header. In addition, the fusing point of the joint bonding material should be well above the melting point of any material ordinarily used to unite fins to tubes. As a component part of the present method, a step has been devised whereby the high fusing bonding material can be successfully brought to its fusing point while maintaining adjacent parts at a relatively low temperature during the fusing operation. This step consists broadly of the application of a cooling medium to parts adjacent the joint being formed and in the preferred form this cooling medium is a bath of water main- .tained at a low temperature and so arranged that any tube or tubes to be connected to a header plate is or are immersed in the bath to a point in close proximity to the face of the plate in which the joint is to be formed. When so positioned, the fusing operation can be carried out without damage to the tubes, or tube-fin bonding, while allowing free flow and fusing of material at the joint and bringing about a complete integra uniting of the ends of the tubes with the header plate.

In the foregoing, more or less specific reference has been made to the jointing of copper tubes to steel headers, but broadly considered the invention is not limited to any particular metal or metals, and the tubes and headers may be of the same metal instead of different metals without departing from the invention. In other words, the present invention contemplates the successful formation of a high temperature joint, that is one capable of standing up and resisting tem peratures of at least as high as 700 F., without breakdown. In the present instance, the high temperature joint completes a unitary heating coil formed of finned tubes by an integral joining of the tubes and headers so that the entire structure is capable not only of resisting all of the strains to which con-' nected tubes and headers are subjected but also temperatures up to approximately 700 F. In the ordinary jointed construction of llt 1 counter-bored holes in a header p tubes and headers, the expansion and contraction causes the joints to open and makes 'The foregoing structure has been made possible by a new and novel method which consists in locating the end of a tube in a prepared hole in a header plate, subjecting the body of the tube to the action of a cooling medium, applying a bonding material having a fusing point as near as possible to the fusing point of the metal of the tube and higher than the annealing point of the tube or any fins carried thereby and Well above the melting point of any material used to unite the fins to the tube or tubes; and subjecting the bonding material, the end of the tube,-and the plate to heat having a temperature higher than the melting point of the bonding material which unites the fins to the tubes.

claim:

1. The method of securing a tube to a header plate where one article is copper and the other is steel, which consists in locating the tube in a hole in the header, subjecting the copper article to a cooling medium to maintain it at a temperature lower than the fusing point of copper, flowing a bondin material having a fusing point substantial y that of copper about the oint between said tube and plate while simultaneously subjecting the two adjacent portions of the two articles to a temperature closely approximating the fusing point of copper.

2. The method of uniting copper tubes to a steel header plate which consists in locating the ends of the tubes respectively in 1prepared ate, subjecting the tubes to a cooling medium to maintain the tubes at a temperature lower than the fusing point of copper, flowing a bonding material having a fuslng point near the fusing point of copper about the joints of said tubes and plates, while simultaneously subjecting the bonding material and the parts to be united to a temperature closely approximating the fusing point of copper.

3. The method of forming a joint between a plate and a tube having fins bonded thereto which consists in su porting the tube with its end in a prepared hole in the plate, subjecting the portion of the tube projecting from said late to a cooling medium to maintain the tu e portion at a temperature below the annealing point of the metal of said tube,

subjecting the tube end and plate surroundof Having thus described our invention, we

ing portion to a temperature higher than the annealing point of the cooled article and simultaneously applying a bonding material having a fusing point approximately that of the metal of the tube and higher than the melting'point of the bonding material between the fins and tube.

4. The method of forming a joint between a plate and the end of a finned tube capable of withstanding temperatures at least as high as 700 E, which consists in locating the end of a finned tube in a prepared hole in a plate, maintaining the finned portion of said tube at a temperature below the annealing point of the tube and below the melting point of any material used to bond the fins to the tube, subjecting the interfitted parts of the tube and plate to a temperature hi her than the annealing point of the metal 0 the tube and plate, and simultaneously applyin to the heated parts a bonding material aving a fusing point substantially the same as the fusing point of the tube metal, but higher than the melting point of the fin bonding material.

Signed at Philadelphia, county of Philadel hia, State of Pennsylvania, this 7th day arch, 1928.

ALEXANDER THORNTON LEWIS. DONALD "E. FRENCH. 

